Sunday Creek Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sunday Creek Observatory clear sky chart from 2005-11-05 to 2017-09-24.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.
Observation TypeMinimum conditions for hour to be usableOut of hours
Clear of CloudsTransparencySeeingSky Brightness
Planetary:50%(no limit)Average(no limit)Nighttime Hours
Deep Sky:70%Average(no limit)5.9Nighttime Hours
CCD Imaging:70%Below AveragePoor(no limit)Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

PlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
Night
30%
15112
10%
46823
7%
15080
34%
15080
14%
35599

By Month

MonthDays of MonthPlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
January1st to 15thNight
18%
898
6%
2685
3%
895
21%
895
7%
2266
January16th to endNight
26%
876
8%
2671
5%
876
29%
876
9%
2222
February1st to 15thNight
27%
704
8%
2287
5%
701
31%
701
11%
1800
February16th to endNight
23%
631
7%
2045
4%
631
28%
631
10%
1648
March1st to 15thNight
24%
720
11%
2011
6%
720
28%
720
13%
1583
March16th to endNight
33%
768
16%
2112
9%
768
38%
768
20%
1537
April1st to 15thNight
28%
668
13%
1764
7%
668
32%
668
18%
1324
April16th to endNight
33%
540
15%
1620
10%
540
38%
540
22%
1116
May1st to 15thNight
35%
414
13%
1494
12%
414
42%
414
17%
1019
May16th to endNight
41%
375
10%
1437
10%
374
48%
374
17%
965
June1st to 15thNight
40%
360
8%
1260
7%
360
42%
360
18%
858
June16th to endNight
43%
360
8%
1260
5%
360
46%
360
22%
815
July1st to 15thNight
45%
340
10%
1190
10%
340
48%
340
23%
744
July16th to endNight
53%
379
13%
1304
15%
357
55%
357
22%
818
August1st to 15thNight
49%
539
10%
1609
7%
536
52%
536
23%
1125
August16th to endNight
46%
573
15%
1719
10%
573
50%
573
24%
1145
September1st to 15thNight
42%
720
12%
1812
6%
720
44%
720
26%
1267
September16th to endNight
46%
693
15%
1930
11%
693
48%
693
25%
1326
October1st to 15thNight
30%
660
13%
1980
10%
660
36%
660
16%
1485
October16th to endNight
24%
704
8%
2171
7%
704
28%
704
10%
1773
November1st to 15thNight
23%
700
10%
2452
8%
700
28%
700
10%
1906
November16th to endNight
21%
720
7%
2520
6%
720
24%
720
8%
2082
December1st to 15thNight
18%
810
5%
2610
1%
810
22%
810
7%
2237
December16th to endNight
15%
960
5%
2880
3%
960
17%
960
5%
2538

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

Occurrence of each ForecastData
Points
Cloud CoverDay
18%10%47%6%35%446%26%
48124
Night
17%12%47%6%34446%26%
46977
TransparencyDay
57%6%11%16%7%
47796
Night
58%6%11%15%6%
46823
SeeingDay
21%9%28%25%11%3
5935
Night
23%7%28%28%9%1
15114

By Month

Percentage Cloud Cover NE (2006-)
Color Meanings:
Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
19%15%7%12%8%345%35%14%
1253
16th to endDay
14%18%7%10%7%35%45%6%16%
1551
February1st to 15thDay
7%15%7%10%9%5%7%45%6%19%
1575
16th to endDay
13%17%10%9%7%33335%21%
1426
March1st to 15thDay
16%12%47%7%35%6%36%26%
1937
16th to endDay
13%10%46%7%35%335%34%
2112
April1st to 15thDay
21%12%47%5%23345%28%
2193
16th to endDay
21%10%36%5%23346%33%
2340
May1st to 15thDay
21%8%36%6%35%45%5%28%
2457
16th to endDay
21%9%36%5%34446%31%
2676
June1st to 15thDay
18%7%37%6%46%5%5%6%27%
2700
16th to endDay
17%6%37%6%36%6%5%8%28%
2700
July1st to 15thDay
15%6%36%5%35%5%6%8%31%
2700
16th to endDay
14%6%36%6%46%46%9%31%
2772
August1st to 15thDay
16%6%35%7%46%6%6%8%27%
2340
16th to endDay
17%7%36%6%36%5%5%8%29%
2471
September1st to 15thDay
19%7%37%5%3445%6%32%
2145
16th to endDay
21%7%36%6%24447%32%
1889
October1st to 15thDay
23%11%36%6%35%44427%
1650
16th to endDay
27%17%6%7%6%3444414%
1700
November1st to 15thDay
22%14%5%9%5%44335%20%
1406
16th to endDay
22%16%7%11%9%3434313%
1440
December1st to 15thDay
19%17%8%9%7%2445%5%14%
1347
16th to endDay
18%18%8%11%8%45%33413%
1344
January1st to 15thNight
18%17%7%12%7%3445%414%
2685
16th to endNight
14%15%5%11%9%45%5%46%16%
2671
February1st to 15thNight
11%13%6%10%9%46%446%20%
2285
16th to endNight
13%18%7%10%7%45%43419%
2045
March1st to 15thNight
16%14%5%9%6%35%445%24%
1999
16th to endNight
14%11%36%6%34436%34%
2112
April1st to 15thNight
21%11%46%5%3235%6%29%
1764
16th to endNight
18%7%45%5%24446%37%
1620
May1st to 15thNight
19%7%345%3446%6%33%
1494
16th to endNight
18%5%36%425%45%8%34%
1435
June1st to 15thNight
18%7%25%5%36%46%6%33%
1260
16th to endNight
13%6%25%6%25%46%6%40%
1260
July1st to 15thNight
13%5%245%25%6%6%8%39%
1260
16th to endNight
12%424435%5%6%8%41%
1393
August1st to 15thNight
14%5%25%5%46%5%6%8%34%
1620
16th to endNight
14%425%5%345%5%7%41%
1719
September1st to 15thNight
15%7%36%43345%6%39%
1812
16th to endNight
18%6%25%233447%39%
1930
October1st to 15thNight
21%11%46%433436%29%
1980
16th to endNight
24%14%48%7%34445%19%
2171
November1st to 15thNight
19%13%6%6%6%35%435%24%
2452
16th to endNight
25%15%6%8%5%24345%18%
2520
December1st to 15thNight
20%17%7%10%8%3433415%
2610
16th to endNight
20%19%7%11%8%35%43411%
2880

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
71%5%6%13%2
1254
16th to endDay
67%5%7%13%6%
1551
February1st to 15thDay
64%5%12%11%6%
1577
16th to endDay
66%26%16%7%
1426
March1st to 15thDay
59%5%9%16%8%
1948
16th to endDay
52%48%21%11%1
2112
April1st to 15thDay
58%48%17%10%1
2193
16th to endDay
52%410%19%12%1
2340
May1st to 15thDay
55%6%8%15%11%1
2457
16th to endDay
53%6%11%17%10%
2680
June1st to 15thDay
54%6%12%18%7%
2700
16th to endDay
52%8%12%18%7%
2700
July1st to 15thDay
45%8%14%22%8%
2541
16th to endDay
49%7%13%24%3
2598
August1st to 15thDay
51%10%16%16%4
2327
16th to endDay
51%8%15%18%5%
2471
September1st to 15thDay
51%7%15%19%6%
2145
16th to endDay
51%7%15%21%3
1889
October1st to 15thDay
59%6%12%14%6%
1650
16th to endDay
74%6%8%7%3
1700
November1st to 15thDay
66%412%11%4
1406
16th to endDay
75%6%8%7%2
1440
December1st to 15thDay
71%5%11%8%3
1347
16th to endDay
76%37%8%2
1344
January1st to 15thNight
71%5%9%10%2
2685
16th to endNight
69%5%8%11%4
2671
February1st to 15thNight
64%412%12%5%
2287
16th to endNight
67%48%13%6%
2045
March1st to 15thNight
63%49%13%8%1
2011
16th to endNight
52%49%17%13%2
2112
April1st to 15thNight
56%38%16%12%2
1764
16th to endNight
48%411%16%18%1
1620
May1st to 15thNight
49%6%10%19%13%1
1494
16th to endNight
48%7%13%17%11%2
1437
June1st to 15thNight
48%6%11%20%10%1
1260
16th to endNight
42%6%14%22%11%1
1260
July1st to 15thNight
38%9%15%25%11%
1190
16th to endNight
40%8%16%27%6%
1304
August1st to 15thNight
44%9%18%22%5%
1609
16th to endNight
41%8%18%25%6%
1719
September1st to 15thNight
43%8%20%19%6%1
1812
16th to endNight
44%6%16%27%4
1930
October1st to 15thNight
56%6%12%16%7%
1980
16th to endNight
67%5%10%12%4
2171
November1st to 15thNight
62%6%13%13%3
2452
16th to endNight
69%6%10%10%3
2520
December1st to 15thNight
73%5%9%9%1
2610
16th to endNight
77%46%7%3
2880

Seeing (when cloud cover <= 80%)
Color Meanings:
Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
28%11%31%20%8%
60
16th to endDay
35%7%24%23%9%
85
February1st to 15thDay
23%7%31%36%1
90
16th to endDay
25%22%35%14%1
81
March1st to 15thDay
20%10%34%26%7%
238
16th to endDay
17%11%36%23%9%2
288
April1st to 15thDay
26%14%21%28%8%1
270
16th to endDay
24%12%28%18%7%7%
270
May1st to 15thDay
30%9%20%20%13%4
288
16th to endDay
24%10%32%22%6%3
389
June1st to 15thDay
21%10%29%26%11%1
495
16th to endDay
15%12%26%29%12%4
495
July1st to 15thDay
16%8%32%28%13%2
475
16th to endDay
15%7%27%29%14%5%
449
August1st to 15thDay
17%421%28%17%10%
313
16th to endDay
22%5%25%19%16%10%
332
September1st to 15thDay
18%426%26%19%5%
315
16th to endDay
21%7%22%28%16%3
287
October1st to 15thDay
26%8%29%25%8%1
255
16th to endDay
31%15%26%20%5%
216
November1st to 15thDay
28%6%43%16%5%
60
16th to endDay
41%20%15%18%5%
60
December1st to 15thDay
26%10%40%20%3
60
16th to endDay
31%17%40%7%3
64
January1st to 15thNight
27%9%31%23%7%
900
16th to endNight
22%8%26%30%10%1
876
February1st to 15thNight
19%8%31%34%6%
704
16th to endNight
23%7%31%28%8%
631
March1st to 15thNight
21%13%33%24%5%
720
16th to endNight
17%10%30%30%9%
768
April1st to 15thNight
27%10%28%26%5%
668
16th to endNight
23%5%31%28%8%1
540
May1st to 15thNight
21%6%29%31%9%
414
16th to endNight
21%6%23%40%7%
375
June1st to 15thNight
22%7%26%32%10%
360
16th to endNight
15%430%35%12%1
360
July1st to 15thNight
15%231%38%11%
340
16th to endNight
15%323%41%13%1
379
August1st to 15thNight
16%222%35%19%2
539
16th to endNight
17%227%33%17%1
573
September1st to 15thNight
19%429%26%18%1
720
16th to endNight
21%5%22%32%15%2
693
October1st to 15thNight
27%7%28%26%8%
660
16th to endNight
33%7%26%23%7%1
704
November1st to 15thNight
26%10%31%24%6%
700
16th to endNight
33%10%25%25%5%
720
December1st to 15thNight
30%8%31%22%5%1
810
16th to endNight
31%9%26%23%7%
960
Page generated at 2017-09-25 09:02:22. Version ac04

Copyright 2017 A. Danko


Sunday Creek Observatory Clear Sky Chart | Charts Home